Wireless Frequency Modulated (FM) radio transmissions are used for several purposes. For example, FM transmissions are used to allow and assist communication in cordless phones, walkie-talkies and baby monitors. One particular use is to use FM transmissions to assist the situation for people being hearing impaired. The equipment commonly comprises a transmitter, which captures a sound from the person speaking, and transmits the sound using an FM signal from the transmitter to a receiver carried by a user. The receiver is able to convert the FM signal to a sound, typically using some type of earpiece, allowing the user to hear the person speaking more clearly. This type of transmission system is crucial to allow the user to handle situations like lectures, meetings, television, radio and theatre.
One problem with the transmission systems in the prior art, is that transmissions may easily be received by non-intended users, preventing private meetings to be held securely. Moreover, because the signal is typically transmitted on a relatively low frequency, large and bulky antennas are required, leading to inconveniently large transmitters and, more importantly, large and bulky receivers.
In transmission systems for hearing impaired persons the hearing impaired person often wears a hearing aid device integrated with the transmission system. this interaction may be accomplished in many different ways. Commonly a hearing loop has been used. The hearing loop is coupled to a receiver which in turn inductively transmits a signal to the hearing aid device of the hearing impaired person. However, the inductive receiver in the hearing aid device may easily receive other magnetic fields than those intended to be picked up by the hearing look. This impairs the audio quality.
One solution to the problem of easily disturbed inductive systems is to directly connect a radio receiver to the hearing aid device. The radio receiver picks up a signal transmitted from the transmission system. Such a connection, a so called audio shoe, is known and is used to connect small mini receivers for direct reception from the transmission system to the hearing aid device.
One problem with such mini receivers is that they are easily disturbed by surrounding electronics, for example by the hearing aid device itself. If these radio disturbances are too large the signal picked up by the mini receiver may be of such a poor quality that the resulting audio of the hearing aid device is unusable, which means that the mini receiver does not function for radio reception from the transmission system.